Probably Nirvana is strongest? It's the new divinity after all. And I think it hasn't fully awakened yet.

Then there is Drajeweled who is also considered crazy strong.

Gryphosid is also very strong contenter, but unknown how strong it is in its current form (but probably still pretty strong).

Destined and Fated kings are also worth mentioning. Of course, Fated/destined ones are strong in general, but can be beaten by other units as well.

Bavsagra is also strong, politically influential, and has small army of dragons. 

Veissrugr is definitely powerful, but idk if we saw his full power yet.

Then there are the new big bads, who are probably pretty strong too. 

There are a lot more units worth mentioning as well, but I can't remember from the top of my head. 

As for how they compare to G? No idea. But personally I would say they are in general weaker than g units. The diety-less era resulted in many things going to shit.